BitWithBite
React · Quick Reference
Lesson 6 — useState Cheat Sheet
In one line: Never mutate state directly — always create a new value and pass it to the setter.
Three State Shapes
1Primitive. const [v,setV]=useState(init);
2Object. setUser(prev=>({...prev,[f]:val}));
3Array Add. setItems(prev=>[...prev,item]);
4Array Remove. setItems(prev=>prev.filter(x=>x.id!==id));
Never Do This
// WRONG — mutates directly
setUser(prev => { prev.name = val })
// RIGHT — spreads into new object
setUser(prev => ({ ...prev, name: val }))